Low duty cycle or impulsive interference is generally defined as interference lasting for a short time relative to the pulse repetition interval (PRF). The PRF is normally on the order of 300 pulses/second. Such low duty cycle or impulsive interference may be caused by a variety of electrical discharges such as, for example, discharges in electrical equipment, and lightning. Such discharges can have a period as short as 0.1 m seconds.
Typical prior art systems for suppressing impulsive interference in MTI signal outputs required the detection of coincidence in two consecutive MTI signal outputs in order to indicate a valid target and not impulsive interference. The non-coincidence of consecutive MTI outputs was assumed to indicate impulsive interference which would then be typically blocked by AND gates. This form of interference suppression with an N pulse MTI system required that the radar remain on the same frequency and the same azimuth angle for at least 2N pulses (N pulses are required for each MTI signal output.) Clearly this 2N pulse requirement decreased the radar data rate capability. Additionally, the requirement for the radar to remain at the same frequency over the 2N pulses significantly limited the radar's ability to employ frequency diversity. As is well known in the art, it is desirable to constantly switch the radar pulse transmission frequency in order to prevent enemy jammers from measuring the pulse frequency and spot-jamming the radar signal.